Field of the Invention
The invention relates to a technology that determines a state of a switch element.
Description of the Background Art
Conventionally, a vehicle, such as a hybrid vehicle and an electrical vehicle, includes a power supply that supplies power to a motor that is a power source. Moreover, a monitoring apparatus that employs a DC voltage application method is known as a monitoring apparatus that monitors a state of the power supply.
The foregoing power supply is configured to be insulated from a vehicle body. Therefore, the monitoring apparatus includes a function of monitoring the insulated state of the power supply, i.e., a function of detecting deterioration of an insulation resistor of the power supply. For example, in the monitoring apparatus, a high pressure battery mounted in the vehicle, a ground of the vehicle body and an insulation resistor for the vehicle are connected in series, and a flying capacitor insulated from the high pressure battery is charged. Then, the monitoring apparatus detects the deterioration of the insulation resistor of the power supply based on a voltage of the charged flying capacitor.
Moreover, since the high pressure battery is configured by a plurality of power supply stacks, the monitoring apparatus includes a monitoring function of monitoring the power supply stacks to prevent overcharge of the power supply stacks and also includes a function of monitoring the monitoring function. The monitoring apparatus monitors the overcharge of each of the power supply stacks by the double monitoring functions, based on the voltage of the flying capacitor connected in series to the power supply stacks.
In these days, a technology has been known that detects a failure of a switch based on a potential difference between output terminals measured when a time period in which a pair of switches configuring an nth pair of series circuits is on is overlapped with a time period in which a pair of switches that are turned on next (refer to, for example, Japanese patent application laid-open publication No. 2009-103546).
However, the foregoing technology connects the power supply stack to an output terminal by overlapping on time periods of the pairs of switches. Therefore, a large voltage is sometimes applied to an output side depending on a voltage of the power supply stack, which may damage an element connected to an output terminal. Thus, it cannot be said that the foregoing technology is not very reliable. Thus, the technology is not a recommended method.